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Abstract
Traditionally associated with memory functions, the hippocampus is now increasingly recognized for its role in language, particularly in reading. This review chapter presents numerous brain imaging and cognitive studies on reading, including studies on healthy participants, people with dyslexia, and neuropsychological patients. These studies demonstrate the necessity of the hippocampus for various aspects of reading, from word decoding to text comprehension. The chapter also explores findings that show how reading practice may contribute to hippocampal development and protection. Given these insights into the deep connections between the hippocampus and reading, it is time to question and potentially redefine the traditional boundaries of the reading network.
Keywords
- hippocampus
- language
- memory
- reading
- neuropsychology
- brain imaging
1. Introduction
The hippocampus is a complex brain structure that remains fascinating even though the frontal cortex partly stole the spotlight from it starting in the 1990s [1]. Its discovery by the Italian anatomist and surgeon Julius Caesar Arantius dates back to the sixteenth century [2]. It was not until the mid-twentieth century that a direct link was established between the hippocampus and memory, particularly through the observation of the effects of bi-hippocampal resection in patient H.M. to treat highly debilitating epileptic seizures [3]. This role was subsequently confirmed in other patients with hippocampal lesions, making this region a key component of the network that underlies declarative memory [4], or even solely episodic memory according to some researchers like Tulving [5].
More recently, since the 1990s, an increasing amount of data has led researchers and clinicians to consider that the hippocampus could also play an important role in language. Thus, for example, a reexamination of data obtained from H.M. suggests that, in addition to memory disorders, he had difficulties understanding language [6, 7]. These language difficulties could also be observed in patients with temporal lobe epilepsy [8, 9]. More recently, Piai et al. have shown, through the recording of electrical activity in the hippocampus, that this structure was involved in language processing [10], leading Covington and Duff to propose extending the ‘classic’ language network to include the hippocampus [11].
In the rest of this chapter, we will present several results suggesting that the hippocampus may also play a significant role in an even more specific activity, reading. This observation raises the question of whether it would be relevant to include the hippocampus in the reading network, which primarily encompasses the ventral occipito-temporal cortex and the lateral fronto-temporal cortex [12].
In light of the simple model of reading [13], we will first explore the potential role of the hippocampus in the identification of individual words, what is called decoding, before examining the stage of understanding sentences and texts.
2. Decoding or the identification of individual words
2.1 In healthy individuals
Before learning to read and being able to correctly identify written words, children spend their first years expanding their vocabulary by learning thousands of new words that they hear. Each of these words corresponds to an arbitrary association between a combination of elementary sounds called phonemes and at least one meaning. In a functional MRI study, Breitenstein et al. showed that healthy adults who activated the hippocampus the most during exposure to new words were also the most successful in expanding their vocabulary [14]. This finding suggests that the hippocampus is involved in the successful learning of new words that are heard. In another fMRI study, Davis et al. highlighted a significant activation of the left hippocampus in healthy adults when they were hearing entirely unfamiliar novel words compared to consolidated and unconsolidated novel words already heard [15]. Moreover, the magnitude of this activation was positively correlated with the post-scan recognition level of these entirely unfamiliar novel words. These results demonstrate that the hippocampus contributes to the initial acquisition of novel spoken words.
When children learn to read from an alphabetic writing system, they first learn to associate each letter with the corresponding sound or phoneme. This process, called grapheme-phoneme conversion, is part of an indirect or graphophonological pathway and requires the co-activation of the visual word form area (VWFA) located in the occipito-temporal cortex, which processes groups of letters, and a temporo-parietal region, which processes the corresponding sounds. These two regions are connected via the posterior segment of the arcuate fasciculus, which significantly develops during the learning of reading as highlighted by diffusion tensor imaging (DTI) [16]. The graphophonological pathway is particularly useful for reading regular words and pseudowords. Using an artificial orthography in an fMRI study, Quinn et al. showed an increase in hippocampal activity between two consecutive days of training to read words using the grapheme-phoneme conversion process with new artificial and arbitrary association rules [17]. The results of an MEG study, in which Finnish adult participants were trained to associate novel foreign letters with Finnish speech sounds, also suggest that the hippocampal region plays a role in this kind of associative learning enabling grapheme-phoneme conversion [18].
He et al. studied 416 healthy Chinese adults and found that a component called ‘form-sound association’ was positively associated with gray matter volume in the bilateral hippocampi [19]. This association was measured using a Visual-Auditory Learning test, which involves forming associations between non-language visual stimuli and oral responses, and a Chinese Vocabulary test, which involves reading 40 very low-frequency Chinese characters. This result confirms the role of the hippocampi in the ability to make connections between a new morpheme visually presented and its sound, which mainly relies on the graphophonological pathway.
Another complementary pathway, the direct or orthographical pathway, is increasingly used as children progress in their reading skills. This pathway starts at the VWFA, which processes groups of letters, and leads directly to the lateral temporal cortex, involved in accessing the semantic information associated with a recognized word from its orthographic form. This pathway is particularly useful for reading irregular words and developing spelling ability.
In an fMRI study [20], Abutalebi et al. compared brain activity in 12 healthy participants while they read dialect words for the first time (from a native language in which participants were illiterate) versus German words (from a second language in which participants were literate). This led to the activation of a network that included the left hippocampus. According to the authors, these findings reflect the contribution of the hippocampus in the development of a new orthographic lexicon by creating associations between meanings and orthographic word forms.
In an fMRI study exploring the effects of a 5-week morpheme-based spelling intervention on children with poor spelling and reading abilities, Gebauer et al. highlighted an increase in spelling and reading comprehension, associated with increased activation in the left temporal, parahippocampal, and hippocampal regions during a lexical decision task [21]. This result reflects the role of these regions in the recollection of a newly learned morpheme-based strategy. It aligns with the findings of Krafnick et al., who observed an increase in gray matter volume in the hippocampus of dyslexic children after an 8-week reading intervention [22].
Sterpenich et al. explored the effects of sleep deprivation on the learning and consolidation of visually processed non-words [23]. Compared to a group of participants who had a sleepless night immediately after learning the non-words, another group who had a full night’s sleep afterward recognized significantly more non-words, with this better recognition being associated with stronger hippocampal activation. These results confirm the role of the hippocampus in the learning of new lexical representations through the mobilization of the two complementary reading pathways, the graphophonological pathway and the orthographic pathway, and demonstrate the detrimental effects of sleep deprivation on these processes.
In an fMRI study, Tao et al. examined the brain changes associated with orthographic word-form learning in healthy adults [24]. The hippocampus showed a significant increase in activity during learning. Moreover, the level of activity in this region was associated with better post-scan recall scores.
Overall, these results suggest that the hippocampus is involved in the learning and consolidation of new words, non-words, or pseudowords that are read.
2.2 In developmental dyslexia
Paz-Alonso et al. studied the effects of dyslexia on brain activations associated with the reading of single words, pseudowords, and pseudohomophones [25]. They observed that lower accuracy in reading pseudohomophones among individuals with dyslexia was associated with reduced activation in the left angular gyrus and hippocampus. This finding reflects the role these regions play in semantic processing during reading. Moreover, during word reading, although there were no accuracy differences between dyslexic participants and controls, dyslexic participants exhibited stronger functional connectivity between the left hippocampus and the
2.3 In patients with temporal lobe epilepsy
Lah et al. conducted a systematic review to examine reading in children with temporal lobe epilepsy [26]. The results show that, overall, patients with temporal lobe epilepsy have lower levels of reading accuracy for regular words, irregular words, and non-words compared to normal controls. Although these results support the view that the hippocampus plays a crucial role in decoding, they do not provide details regarding the specific processes associated with decoding that are impaired.
2.4 In patient H.M
MacKay and James found that patient H.M. suffered from deficits in reading low-frequency words and pseudowords aloud [27]. This result has been interpreted as reflecting the crucial role of the hippocampus in creating new connections between nodes or representational units located at the semantic, phonological, or orthographic levels.
2.5 In patients with Alzheimer’s disease
Ota et al. evaluated language abilities in 22 patients with Alzheimer’s disease [28]. They found significant negative correlations between a score for reading aloud Kanji words and small-world properties (reflecting structural brain networks) in several brain regions, including the bilateral hippocampi. This means that as the reading score decreases, the functions of the highlighted regions become segregated from their surroundings. The authors interpreted this result as reflecting the crucial role of the hippocampi in semantic processes during the reading of Kanji words.
3. Comprehension
3.1 A cognitive model of comprehension
According to one of the most influential models in the cognitive sciences of reading, the Construction-Integration model [29, 30], two forms of representations are activated during reading and text comprehension: (1) the text base and (2) the situation model. The text base includes surface elements (each individual word consisting of an association between a combination of letters and one or several meanings, and the way these words are ordered according to specific syntax) and semantic propositions (associations between a predicate, most often a verb, and one or several arguments, typically nouns). The text base primarily relies on the information contained within the text itself, whereas the situation model involves integrating this information with the reader’s memories and knowledge. Therefore, the situation model is likely to differ between readers, while the text base remains relatively consistent across readers. These two forms of representations are activated during the reading of a text, ultimately leading to the construction of a global representation known as the episodic text memory. The representations described here will be referenced in some of the articles presented below.
3.2 At the sentence level
3.2.1 In healthy individuals
In an fMRI study, Cooke et al. measured brain activity while students were reading sentences differing in their grammatical structure [31]. They observed activation of the left hippocampus when contrasting object-relative long antecedent-gap sentences with a pseudofont baseline, and when contrasting object-relative long antecedent-gap sentences with subject-relative long antecedent-gap sentences. At the time, the authors had no precise explanation for this new result. It may have reflected the possible role of this region in single-word processing during lexical encoding and in lexical meaningfulness. However, it seemed unlikely to the authors at the time that this region had a linguistically specific role.
In a Positron Emission Tomography (PET) study, Waters et al. explored the brain regions involved in syntactic processing during the comprehension of written sentences [32]. Participants were divided into two groups based on their sentence processing speed. When contrasting syntactically complex subject-object sentences with syntactically simple object-subject sentences, the authors found that only participants with low processing speed activated several regions, including the right hippocampus. According to the authors, this result was not easily explicable and may reflect the use of visual imagery.
Hoenig and Scheef studied the role of the medial temporal lobe in semantic processing [33]. Twenty-two participants performed a context verification task, making decisions about the semantic fit of congruent and incongruent target words with the overall meaning of preceding sentence contexts. Half of the sentences ended with an ambiguous (homographic) word. The study followed a 2 × 2 factorial design with four experimental conditions: CH (congruent homographic), CN (congruent neutral), IH (incongruent homographic), and IN (incongruent neutral). All these conditions, requiring semantic context verification, resulted in significant activation of a network including the bilateral hippocampi. This region may ‘contribute to semantic processing by a mnemonic function that serves to link the target meaning representation with the meaning of a prior sentence context’. A conjunction analysis of the contrasts IH minus IN and CH minus CN yielded significant activation in several left hemisphere regions, including the parahippocampal gyrus. This region may then play a role in the processing of semantic ambiguity.
Using an artificial language, Opitz and Friederici explored the brain regions involved in detecting long-distance and local syntactic violations [34]. Twenty-three participants, previously trained in the new grammar system named BROCANTO, read sentences that were either grammatical or ungrammatical. The authors found that the hippocampus was significantly activated in response to violations of local syntactic dependencies. This result is interpreted as reflecting that a local syntactic violation ‘introduces a new relationship between a particular word and its new syntactic role in a sentence’, which may require ‘increased relational processing demands’ mediated by the hippocampus.
Lee and Newman studied the effects of two different sentence presentation paradigms—rapid serial visual presentation (RSVP) and whole sentence presentation—on syntactic processing [35]. Twenty participants read single sentences presented either as a whole on a screen or one word at a time in the middle of the same screen. After reading each sentence, a probe was presented to evaluate comprehension. Comprehension accuracy was significantly higher for sentences presented as a whole. Several regions, including the bilateral hippocampi, were significantly more activated during the reading of sentences presented as a whole compared to those read in RSVP. This result may reflect the role of the hippocampi in a relational binding process, integrating items into a cohesive memory representation, which may be limited during RSVP.
Prat and Just investigated the relationships between interindividual differences in working memory capacity and brain activity during a sentence comprehension task with varying syntactic complexity [36]. They found a positive correlation between working memory capacity and the activation level in several brain regions, including the left hippocampus, when comparing complex sentences to simple ones. In simple terms, participants with higher working memory capacity activated several brain regions more intensely while reading syntactically complex sentences, with the hippocampus specifically associated with memory function in this context.
Citron and Goldberg measured brain activity in 26 participants while they were reading metaphorical sentences [37]. By comparison to literal sentences, metaphorical sentences were associated with the activation of a brain network that included the left hippocampus. Along with the amygdala, which was also activated, the hippocampus may contribute to the memory encoding and/or retrieval of emotional information that occurs while reading metaphorical sentences.
Bonhage et al. explored the brain signature of working memory for sentence structure [38]. Among several contrasts, they compared brain activity measured while 18 participants were reading and encoding sentence fragments to brain activity measured during a baseline condition involving the reading and encoding of ungrammatical word strings. They found that a network of brain regions, including the bilateral hippocampi, was significantly activated. This result may reflect the role of the hippocampi in enriching the information in sentences with semantic information stored in long-term memory. The authors refer to the work of MacKay et al., showing that patient H.M. ‘was unable to recognize ambiguities in sentences’, a result ‘interpreted as reflecting a specific deficit regarding semantic-level binding’ [6]. Another complementary explanation is based on results showing an involvement of the hippocampus in syntax processing [39], specifically in detecting syntactic violations after predictive processing, which cannot apply when reading ungrammatical word strings.
A year later, Bonhage et al. used a combination of eye-tracking and fMRI techniques to identify brain regions involved in linguistic predictions via anticipatory eye movements [40]. The correct prediction of the syntactic word category (verb/noun) of a target that would appear after reading a regular sentence or a meaningless jabberwocky sentence was associated with significant activation of several brain regions, including the bilateral hippocampi. This result may reflect the role of the hippocampus in predictive processing at a syntactic level. The finding that the bilateral hippocampi were also significantly more activated for regular sentences than for jabberwocky sentences underscores the role of this region in predictive processing at a lexical-semantic level. These results are considered in light of the predictive coding model [41], which may apply to linguistics. As stated by Ryan and Shen, the use of eye-tracking is highly relevant for studying memory because the oculomotor system is well connected to the hippocampal memory system [42]. By extension, eye-tracking is particularly valuable for studying the role of the hippocampus in reading, as this cognitive ability relies on the complex exploration of sentences and texts through numerous saccades and fixations. These eye movements contribute to the emergence of meaning, in connection with the hippocampus.
In another study combining eye-tracking and fMRI techniques, Schuster et al. explored the effects of word length, frequency, and predictability on brain activity while 56 healthy participants read sentences [43]. Sentence reading was associated with the activation of a large network of brain regions including the hippocampus. There was also a significant negative correlation between the frequency of the words in the sentences and activation in several regions, including the left hippocampus. In simple terms, activity in this region decreased as word frequency increased. However, the authors did not specifically interpret this correlation with the left hippocampus, only considering its well-known role in memory encoding and retrieval. Notably, the predictive coding model [44] was proposed to interpret a negative correlation obtained in the left occipito-temporal cortex, which encompasses the VWFA. Considering the previous study described above, this model could also apply to the left hippocampus.
Pu et al. used a combination of magnetoencephalography (MEG) and eye-tracking techniques to investigate the specific roles of hippocampal theta oscillations in language processing [45]. They found increased theta power in the hippocampus when healthy participants read sentences ending with a semantically incorrect word, which was not the case when sentences ended with a syntactically incorrect word. These results highlight the critical role of the hippocampus in semantic processing during reading. More precisely, the hippocampus could be involved in ‘semantic retrieval and prediction based on previous knowledge’ (see above) and in an integration process, given that a semantic violation of the last word increases the difficulty of integrating the meaning of the upcoming words into the meaning built up during reading.
In a study combining eye-tracking and fMRI techniques, Schuster et al. investigated the brain regions involved in predictive processing during reading [46]. They presented 39 healthy participants with sentences that ended with a target word that was either congruent or incongruent with the preceding context and had either high- or low-cloze probability. The right hippocampal region was significantly more activated for low-cloze compared to high-cloze sentences in congruent sentence endings. This result was interpreted as reflecting the contribution of this region to language processing and the assembly of semantic meaning by relating incoming words to stored semantic information.
3.2.2 In patients with epilepsy
McCarthy et al. evaluated 64 patients with complex partial epilepsy for resective surgery to relieve intractable seizures [47]. Intracranial electrodes were implanted to localize the seizure foci. Recordings were obtained from these electrodes while the patients were reading sentences. Half of the sentences presented to the patients ended normally, while the other half ended with a semantically anomalous word. The authors found that ‘anomalous sentence endings often, but not always, elicited a large negative field potential in the hippocampus’. These results are coherent with those obtained in healthy subjects and described above. They confirm the role of the hippocampus in semantic processing whether it is involved in semantic retrieval, prediction, or integration.
Noppeney et al. explored the compensatory mechanisms associated with good reading skills in patients after left anterior temporal lobe resection for mesial temporal lobe epilepsy [48]. Brain activity was measured using fMRI while 16 patients read nine-word sentences. Reading ability was significantly and positively correlated with activation levels in several regions, including the right hippocampus. Furthermore, in controls and in patients with a reading ability within the normal range, activations were found in the right hippocampus and inferior temporal cortex. The authors interpret this result as indicating that patients with high reading skills might engage more in encoding sentences using the right hippocampus. Additionally, this result suggests that patients without a functional left anterior hippocampus rely on the right hippocampus to maintain proficient reading skills.
3.2.3 In patient H.M.
In a series of four experiments, MacKay and James evaluated patient H.M.’s sentence reading abilities using novel sentences composed of high-frequency words [49]. In all these experiments, patient H.M. produced more misreadings than controls. These misreadings were associated with reduced semantic and syntactic complexity, leading to ungrammaticality. These results were interpreted in light of Node Structure Theory [50] and may reflect the crucial role of the hippocampus in binding or creating new connections between nodes.
3.3 At the text level
3.3.1 Functional brain imaging data obtained in healthy participants
To our knowledge, the first study to observe hippocampal activation during text reading was published in 2005 by Xu et al. [51]. In this fMRI study, 22 right-handed healthy participants with an average age of 34 years were instructed to read Aesop’s fables in 46-second blocks. Brain activity measured during this main task was compared to activity measured while the same participants read random consonant letter strings. Among other regions, the left hippocampus was significantly activated during the main task compared to the baseline task. The authors interpreted this result by suggesting that the hippocampus might play a role in either memory encoding or retrieval, which implicitly refers to episodic memory, or in the implicit activation of semantic associations as the story unfolds.
In another fMRI study, Ferstl and von Cramon explored the neural substrates of the temporal, spatial, and emotional dimensions of situation models constructed by 20 healthy subjects while reading short narrative texts comprising two sentences [52]. The comparison of brain activity associated with processing the ‘spatial’ dimension of the situation model with brain activity associated with processing the ‘emotional/temporal’ dimensions highlighted the activation of the precuneus/posterior cingulate cortex and the hippocampal region. The activation of this latter region has been interpreted as reflecting its involvement in memory and navigation processes concerning spatial information contained in a situation model.
The same interpretation was proposed by Mano et al. to explain why the hippocampal region was activated in 18 healthy adults while they were reading a narrative text that required processing the emotions of protagonists [53]. This again suggests that this region is involved in the processing of spatial information during narrative comprehension.
In an fMRI study aimed at exploring the neural substrates of analogical reasoning during metaphor comprehension, Prat et al. asked 24 healthy right-handed participants with varying levels of working memory to read three-sentence passages with different processing demands [54]. Unlike several cortical regions, which were activated based on the processing demands of the task, the hippocampus was activated in a similar manner regardless of these demands. This suggests that the hippocampus is recruited as soon as reading and metaphor comprehension are involved, regardless of task difficulty. Furthermore, there was a positive correlation between the participants’ working memory capacity and the level of activation in the hippocampus as a function of the supportive context provided. This indicates that participants with higher working memory capacity activate the hippocampus more when the supportive context can be particularly exploited, suggesting a role for the hippocampus in the flexible use of ‘working semantic memory’ during metaphor comprehension.
Aboud et al. found, in adolescents aged between 9 and 14 years, a positive correlation between activation levels of the left hippocampus (among a larger network) during the reading of documentary texts and the comprehension scores measured thereafter [55]. This result was interpreted as indicating that the best readers, in terms of reading comprehension, have better inferential processing capabilities supported by those regions associated with the default mode network, of which the hippocampus is a part.
Helder et al. showed that in a group of healthy adult participants, the detection of incoherency when reading the sixth and last sentence of a text was accompanied by the activation of a network that includes the hippocampus [56]. The authors suggest that the hippocampal activation could reflect the ‘reactivation of episodic memory traces of the text or reactivation of background knowledge’ in an attempt to restore coherency, as well as the episodic encoding of this particular situation.
In an fMRI study exploring the brain regions involved in coherence monitoring during the reading of documentary texts, Van Moort et al., asked 31 healthy participants to read 10-sentence-long texts about well-known historical topics [57]. These texts included a target sentence that was either true or false based on the readers’ background knowledge. Comparing brain activity measured during the reading of a true target sentence versus a false target sentence highlighted significant activation in several regions, including the left hippocampus. This sensitivity of the left hippocampus to the ‘correctness’ of information with respect to background knowledge, while a dorso-medial prefrontal region was significantly more sensitive to the ‘incorrectness’ of information, suggests that a network involving these two regions is engaged in knowledge-based processing. The dorso-medial prefrontal region would ‘detect erroneous world-knowledge information and signal to the hippocampus that existing knowledge structure should not be updated’, while the hippocampus would be involved in the ‘normal’ integration processes between what is read and background knowledge.
In a study using eye-tracking, electroencephalography (EEG), and fMRI, Sato et al. explored the mnemonic neural dynamics associated with the natural reading of literature [58]. One of the experiments involved 19 participants reading two essays at a natural pace inside an MRI scanner for 10 minutes. The fMRI results showed negative correlations between brain activity in several regions, including the left hippocampal region, and text correlation scores that reflect the relationship between the content of the read texts and the content reports subsequently written by the participants. This indicates a negative subsequent memory effect for the left hippocampal region, which is unusual since this region is more often associated with a positive subsequent memory effect. The authors suggest that this result may be explained by the long duration of the reading task (10 minutes) and cite a study in which the hippocampus was activated only at the end of an event, while the average activity in this region decreased during the event.
Interestingly, Saito et al. found similar paradoxical results in their study [59]. They compared brain activity between a group of 23 rapid readers and a group of 23 non-rapid readers while reading novels during 60-second blocks (compared to a low-level cross-fixation baseline task). Both reading speed and comprehension scores were higher in rapid readers than in non-rapid readers. During reading, brain activity was significantly lower in rapid readers than in non-rapid readers in several regions, including the hippocampus. Additionally, there was a significant negative correlation between reading speed and activity in these same regions. The authors interpret these results as reflecting the ability of rapid readers to reduce language processes, such as phonological, semantic, and syntactic processes, while maintaining reading comprehension during rapid reading.
In a recent fMRI study aiming to identify the brain regions associated with the level of comprehension of documentary texts, Keller et al. asked 31 healthy participants, with either high or low comprehension skills, to read 65-sentence-long texts three times each [60]. The participants then completed a comprehension test based on multiple-choice questions. Several positive correlations were found between comprehension scores and activity measured during the reading of the texts in various brain regions, including the bilateral hippocampi. This result was interpreted as reflecting the role of the hippocampi in the episodic encoding and consolidation of new declarative knowledge. More precisely, during the reading of texts, this region may enable the encoding and integration of new semantic information from the texts with pre-existing semantic knowledge to construct new knowledge structures.
3.3.2 Brain imaging data obtained in patients
In an fMRI study [61], Malfait et al. investigated the brain regions activated while 19 children (mean age of around 11 years) with benign epilepsy with centro-central spikes (BECTS) read pairs of syntactically complex sentences. They were asked to decide whether the second sentence of each pair was true or false with respect to the first sentence. Performance on this task was comparable between children with BECTS and a control group. During this reading task, in addition to several brain regions commonly activated by both groups, children with BECTS also activated other regions, including the left hippocampus. According to the authors, this additional activation of the left hippocampus was unexpected. They consider its well-known association with memory systems and its more specific role in grapheme decoding, as demonstrated by He et al. (see above) [19].
To our knowledge, the first study to explore the brain structures necessary for text comprehension and memorization was conducted by Hausser et al. using a combined VBM/DTI approach in neuropsychological patients [62]. In this study, comprehension scores (text base and situation model) were obtained after the patients read narrative texts. The results show that the hippocampal region, in connection with the uncinate fasciculus (known to play a role in semantic processing), and the fornix and ventral cingulum (known to play a role in episodic memory), is essential not only for retrieving the text base and the situation model through episodic memory but also for activating the text base during reading and comprehension.
4. The effects of reading practice and literacy on the hippocampus
Sumowsky et al. explored the contribution of various types of cognitive leisure activities to cognitive reserve in patients with multiple sclerosis [63]. The results showed that greater engagement in reading and writing activities was positively correlated with larger hippocampal volume and better memory levels. According to the authors, ‘most knowledge acquisition after high school is accomplished through literacy (i.e., reading), which may explain the relationship between reading-writing activity and hippocampal volume reported herein’. These valuable findings thoroughly ‘inform the development of targeted evidence-based enrichment programs’ aimed at bolstering reserve against memory decline.
In a study published by Sun et al. in
5. Conclusions
This chapter provides a comprehensive exploration of the hippocampus’s role in reading, traditionally viewed as a memory-related brain structure. Through an extensive review of brain imaging and cognitive studies in various populations, the hippocampus is established as a crucial component in reading. Key findings highlight its involvement at various stages of reading, from word decoding to text comprehension via sentence comprehension. At the decoding level, the hippocampus is actively engaged in learning grapheme-phoneme associations, orthographic word forms, associations between orthographic word forms and meanings, and forming connections between semantic, phonological, and orthographic units. At the sentence level, the hippocampus plays a significant role in syntactic processing and semantic processing, including semantic prediction and integration. At the text level, the hippocampus is involved in the harmonious use of semantic and episodic memory systems, as well as in inferential processing, enabling readers to create and memorize the text base and situation model that contribute to a coherent episodic text memory. Moreover, this chapter examines how reading practice contributes to hippocampal development and protection. In conclusion, this chapter provides compelling evidence that the hippocampus should be considered an integral part of the reading network. Recognizing its role enhances our understanding of reading’s cognitive and neural mechanisms and emphasizes the importance of reading practices in educational, developmental, and therapeutical strategies. This perspective advocates for continued research and practical applications in education and neurocognitive health.
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